1. Field of the Invention
The present invention relates to a head-mounted display and the like, and more particularly, to an image display apparatus and an image display method by which a person can view a clear image with the naked eye.
2. Description of the Background Art
An image display apparatus as typified by a head-mounted display (hereinafter, referred to as an HMD) is a mobile display terminal for personal use, and has an eyeglass-shaped structure for easy wearing.
Here, there are individual differences in human eyes (eyesight, curved shape of retina, etc.), and failure of image formation on the retina may occur due to the individual differences.
As a technology for eliminating the above failure of image formation to obtain a desired image formation state, for example, there is a technology disclosed in Japanese Patent Laid-Open Publication No. H07-128613. In the technology in Japanese Patent Laid-Open Publication No. H07-128613, a liquid crystal display, a light source constituted of an LED array, and a light blocking element for blocking a part of light incident on a detector are arranged at optically conjugate positions, and a magnifying lens for magnifying an image is driven by using a lens driving section. Thus, a desired image formation state on a retina can be constantly obtained, thereby reducing the fatigue of an eye.
Further, as another technology for eliminating the above failure of image formation to obtain a desired image formation state, for example, there is a technology disclosed in Japanese Patent Laid-Open Publication No. 2001-27740. In the technology in Japanese Patent Laid-Open Publication No. 2001-27740, prisms are arranged as light deflection means for the X axis and Y axis, respectively, and automatic focus adjustment is performed by driving a light collection optical system using optical system driving means, and hence, a desired image formation state on a retina can be constantly obtained. Thus, the technology in Japanese Patent Laid-Open Publication No. 2001-27740 can eliminate the need for optical adjustment (visibility, aberration correction, etc.) in accordance with characteristics of eyes, such as shortsightedness, farsightedness, astigmatism, and the like.
Further, although not being a technology for eliminating the above failure of image formation to obtain a desired image formation state, for example, there is a technology disclosed in Japanese Patent Laid-Open Publication No. H11-197109 as a technology for scanning laser ophthalmoscopes. In the technology in Japanese Patent Laid-Open Publication No. H11-197109, the focus position of laser light is adjusted to a predetermined area of a tested eye by mechanically moving an optical system, which includes a laser light source and a scanning section, while maintaining an optically conjugate relation of a galvanometer mirror constituting the scanning section with the pupil of the tested eye. Thus, in the technology in Japanese Patent Laid-open Publication No. H11-197109, a confocal optical system can be constituted of a simple optical system and a movement mechanism, and a scanning laser ophthalmoscope with remarkably improved image contrast and resolution can be provided at a low cost.
In any of the conventional technologies described above, reflected light from a retina is detected for performing focus adjustment of scanning light. Further, the conventional image display apparatuses described above adjust an image formation state on the retina by detecting the reflected light from the retina and adjusting the focus of the scanning light. Here, even when the scanning light is incident on the retina from the view line direction (the front direction of an eyeball) of a viewer (a user whose eye is scanned), namely, even when specularly reflected light from the retina is obtained, the amount of the reflected light from the retina is very small. Further, when the scanning light is incident on the retina from the direction inclined at an angle with respect to the view line direction of the viewer, namely, when specularly reflected light from the retina is not obtained, the amount of the reflected light from the retina is extremely small. Thus, in the conventional technology, detection error of the reflected light from the retina is large, and hence, the focus adjustment of the scanning light may not be performed accurately and an image formation state on the retina may not be adjusted accurately. Further, particularly, in the peripheral visual field of the user in which specularly reflected light is not obtained from the retina, an image formation state on the retina may be not adjusted.